12 research outputs found
Racine, a creative artist: a study of his women characters as contrasted with their Biblical and classical prototypes
Thesis (M.A.)--Boston University, 1917. This item was digitized by the Internet Archive
Generalized parton distributions of the pion: modeling, evolution and observable implications
Yet the Standard Model of particle physics is so far the most successful theory ever conceived in
science, with countless of achievements in the description of Nature; still a number of phenomena
remains to be properly understood. A paradigmatic example is confinement. Paving the road
towards the understanding of such essential feature thus requires a detailed knowledge of hadrons'
inside. The main subject covered in this thesis is precisely the study of hadron structure.
Nonetheless this is a really broad field. We thus set sights on an exemplary case: The pions. As
mesons, they are potentially simpler to describe that other hadrons like the proton. At the same
time, as the pseudo Nambu-Goldstone modes associated to the dynamical breakdown of chiral
symmetry, its description is of uttermost relevance for the comprehension of the origin of mass in
Nature. We thus address the problem of assessing pions' structure, from first principles up to its
observable manifestations.
This work is thus divided into two parts: First, the issue of a formal description of hadron's structure
is addressed. Relying on the role played by Compton scattering as an essential window into
hadrons' inside, we review its formal treatment as understood in the generalized Bjorken limit,
leading to the introduction of generalized parton distributions (GPDs). Those parametrize the
amplitudes for deeply virtual Compton scattering (DVCS) on hadrons to take place, yielding a
unique source of information about the way hadrons are built up from elementary constituents. In
the second chapter of this dissertation we review the formal definition and primary properties of
generalized parton distributions, together with the main strategies allowing for their evaluation. We
identify two essential attributes to be fulfilled: Positivity and polynomiality; a task which,
regardless, conventional approaches fail to accomplish. In the third chapter of this thesis we face
the problem of obtaining models for pion GPDs which fulfill, by construction, these two features.
Following an approach to the description of bound-state systems in quantum field theory based on
continuum Schwinger methods, we find the hypothesis of decoupling between longitudinal and
transverse degrees of freedom at the level of parton dynamics to be associated with the dynamical
breakdown of chiral symmetry. On that assumption, a novel family of generalized parton
distributions within the DGLAP region is derived and showed to exhibit two striking characteristics:
They satisfy the positivity constraints, and are built from the sole knowledge of parton distribution
functions. From that point on we exploit the covariant extension strategy, allowing us to find the corresponding ERBL GPDs, such that polynomiality is also fulfilled by construction.
Armed with models for pion GPDs that are complete, in the sense that they satisfy every necessary
property, the second part of this work thus exploits them in the derivation of their observable
manifestations, allowing for a practical assessment of pions' structure as well their benchmarking.
To this end, the fourth chapter pursues the necessary evaluation of scale-evolution for GPDs
through an effective approach which encompasses some non-perturbative aspects of the
procedure. The results hint the crucial role played by gluons in building pions' up, their associated
distributions being commensurate with those for quarks. We thus round-off this dissertation by
exploiting the evolved models to deliver predictions on event-rates and beam-spin asymmetries as
they could be measured at forthcoming electron-ion colliders. The results reveal that indeed DVCS
on pions is expected to be measurable at future facilities; and reveals that gluons dominate the
response of pions subjected to DVCS, identifying a sign inversion in the beam-spin asymmetries as
clear signal for pinning-down the regime for gluon dominance.Pese a la ingente cantidad de resultados derivados del Modelo Est谩ndar de la f铆sica de part铆culas
a煤n existe una gran cantidad de fen贸menos que no llegamos a entender completamente. Un
ejemplo es el del confinamiento. Un paso esencial para su comprensi贸n es la descripci贸n de la
estructura hadr贸nica. Esta es precisamente la tem谩tica de esta tesis, donde se estudia la
estructura de piones mediante el formalismo de las distribuciones generalizadas de partones
(GPDs, por sus siglas en ingl茅s). Como mesones, los piones deber铆an ser m谩s sencillos de describir
que otros hadrones como el prot贸n. M谩s a煤n, debido a su naturaleza dual como estados ligados
pero tambi茅n como bosones Goldstone asociados a la rotura din谩mica de simetr铆a quiral, los piones
son una pieza fundamental para comprender el origen de la masa en sistemas f铆sicos. Por todo
esto esta tesis aborda la descripci贸n de la estructura pi贸nica a primeros principios y eval煤a sus
manifestaciones en experimentos.
El trabajo est谩 dividido en dos partes. Empezando por abordar el problema de la descripci贸n de la
estructura hadr贸nica desde una perspectiva general, el primer cap铆tulo revisa los procesos de
scattering Compton en este sentido. As铆, la identificaci贸n del l铆mite de dispersi贸n profundamente
virtual permite la introducci贸n de las GPDs como objectos fundamentales para la descripci贸n de
scattering Compton profundamente virtual (DVCS, en ingl茅s). El segundo cap铆tulo se dedica
entonces a un an谩lisis detallado de estas, empezando por su definici贸n, propiedades y una
discusi贸n detallada sobre toda la informaci贸n que codifican sobre la estructura hadr贸nica. En este
proceso se encuentra que las llamadas propiedades de "polinomialidad" y "positividad" juegan un
papel central en la construcci贸n de modelos de GPDs realistas, y es por tanto satisfacerlas en todo
caso. En este sentido es importante destacar que las estrategias convencionales para el c谩lculo de
GPDs no consiguen este objetivo. Con ello, el tercer cap铆tulo de la tesis aborda el problema de
construir modelos de GPDs para piones que satisfagan, por construcci贸n, ambas propiedades.
Siguiendo una estrategia basada en el m茅todo de las ecuaciones de Dyson-Schwinger para la
descripci贸n de estados ligados, se encuentra que la hip贸tesis de desacoplo entre los grados de
libertad longitudinales y transversales de la din谩mica part贸nica est谩 铆ntimamente relacionada con
la restauraci贸n de la simetr铆a quiral. Explotando dicha hip贸tesis derivamos una nueva familia de GPDs en la regi贸n DGLAP que satisfacen la condici贸n de positividad y para cuya construcci贸n
煤nicamente es necesario el conocimiento de las llamadas funciones de distribuci贸n de partones.
Partiendo de ese resultado, la estrategia de extensi贸n covariante permite obtener la
correspondiente regi贸n ERBL, obteniendo por primera vez modelos de GPDs que satisfacen al
mismo tiempo y por construcci贸n las condiciones de positividad y polinomialidad. Con el fin de arrojar luz a nuestro entendimiento sobre la estructura de los piones, as铆 como la
contrastaci贸n de este estudio, la segunda parte del trabajo parte de los mencionados modelos y
eval煤a sus manifestaciones en los resultados obtenidos en futuros experimentos. Para ello, el
cap铆tulo cuatro se encarga de describir la necesaria evoluci贸n de GPDs con la escala de
renormalizaci贸n; implementando una estrategia efectiva capaz de abarcar efectos puramente no
perturbativos de la interacci贸n fuerte. Los resultados ponen de manifiesto el importante papel del
contenido glu贸nico en la construcci贸n de la estructura de piones. Finalmente, el quinto cap铆tulo
describe el c谩lculo de n煤mero de eventos y asimetr铆as en futuros aceleradores electr贸n-ion,
mostrando que efectivamente estas instalaciones deber铆an ser capaces de medir DVCS en piones e
identificando la inversi贸n en las correspondientes asimetr铆as como una clara se帽al experimental
capaz de delimitar el r茅gimen en el que los gluones constituyen la parte dominante en la
estructura pi贸nica
The Advocate - June 25, 1964
Original title (1951-1987)--The Advocate: official publication of the Archdiocese of Newark (N.J.)
Human factor influences on effective computer aided design implementation.
Computer Aided Design (CAD) has the capability to influence a company's competitiveness in terms of quality, flexibility and cost effectiveness of design. Consequently, the opportunities provided by the efficient and effective use of CAD techniques are vital to a company's operational and business success.The aims of this research have been to; 1 Ascertain and identify the contribution and relevance of human factor and technological issues within a successful CAD implementation methodology. 2. Develop a human factor understanding which, when incorporated into an implementation methodology aids the introduction of CAD technology and increases the likelihood of realising opportunities. The initial research is based on a review of the literature on CAD and a pilot study of six companies employing CAD. This identifies the mix of issues involved during implementation as being, Technical, Organisational and Human. It also highlights the main problems experienced by companies as a function of the levels of Support, Direction and Communication. The above issues have been incorporated into a CAD introduction framework based on quality criteria. The results of this initial stage of the research have been substantiated by in-depth case studies of three companies, in various stages of CAD adoption and "Best Practice" activities have been identified for each area of the framework and related to the overall performance of the companies.To widen the scope of the investigation and provide more evidence, the framework was then employed in the in-depth analysis of six further case studies. These identified CAD support as playing a key role in maximising CAD potential.From this evidence a "Support Framework" has been proposed and validated via the results of a written postal questionnaire distributed to 1000 UK companies. Evidence from the 100 respondents of the postal survey strongly supports the proposition and suggests that companies are experiencing human problems, especially in the area of advanced 3D CAD. The problems are a result of inadequate internal support systems and can be overcome by the methods proposed by this research